The present invention is concerned with image analysis and more particularly with extracting three-dimensional information from a two-dimensional image.
Perspective is present to some extent in all images that reflect 3D information. Parallel lines in the three dimensional scene project to vanishing points in the image. Locating the vanishing points provides a powerful way of inferring 3D structure from a 2D image especially in a landscape or a man-made environment. Lutton et al [1] extract edges and assemble line segments which point towards vanishing points. This approach requires knowledge of camera parameters and has to deal with large numbers of very short segments arising from certain images. McLean et al [2] cluster gradient orientations to again detect line structure in images and evaluates the method against two grey level images. Along with other authors Shufelt [3] uses a Gaussian sphere representation and addresses the problem of spurious edges in images with a limited range of object orientations.
Rother [4] applies the ideas to architectural environments and rejects falsely detected vanishing points by making use of camera parameters. Cantoni et al [5] explores two approaches, one using the Hough transform and the other edge detection. Successive analyses are required to locate multiple vanishing points. Almansa et al [6] proposes a method not dependent on camera parameters which searches for image regions that contain maximum numbers of line segment intersections. Curved boundaries in images that do not contain actual vanishing points can cause false alarms. Gabor wavelet filters are used by Rasmussen [7] to obtain dominant texture orientation in images of roads.
Some techniques for analysis of images or other patterns where the pattern is compared with other parts of the same pattern are described in our earlier patent applications as follows.    European patent application 00301262.2 (publication No. 1126411) (applicants ref. A25904EP#);    International patent application PCT/GB01/00504 (publication No. WO 01/61648) (applicants ref. A25904WO);    International patent application PCT/GB01/03802 (publication No. WO02/21446) (applicants ref. A26055WO);    U.S. patent application Ser. No. 09/977,263 filed 16 Oct. 2001 (publication No. 20020081033) (applicants ref. A25904US1);    International patent application OPCT/GB2006/002001 (A30776).            as well as the following papers published by the inventor:            Stentiford F W M, “An estimator for visual attention through competitive novelty with application to image compression”, Proc. Picture Coding Symposium 2001, Seoul, 25-27 April, pp 101-104, 2001.Stentiford F W M, “An evolutionary programming approach to the simulation of visual attention”, Proc. Congress on Evolutionary Computation 2001, Seoul, pp 851-858, 27-30 May, 2001.
Methods and apparatus for comparing patterns are described in our earlier international patent application WO03/081523 (A30179) and our U.K. patent applications 0420727.0 dated 17 Sep. 2004 (A30519) and 0503944.1 dated 25 Feb. 2005 (A30705).
Aspects of the present invention are set out in the claims.